Automatic spraying techniques have long been employed for painting large articles such as cars, trucks, refrigerators, etc. The items being sprayed are generally advanced along a conveyor line which passes through a water wash paint spray booth where a fine spray of paint is directed at the articles being painted from spray guns which are located at the sides of the conveyor. Overspray paint, that is, paint which does not contact the article being painted, forms a fine mist of paint in the air space surrounding the painted article. This paint mist must be removed from the air. To accomplish this, the contaminated air is pulled through the paint spray booth by air exhaust fans. A curtain of circulating water is maintained across the path of the air in a manner such that the air must pass through the water curtain to reach the exhaust fans. As the air passes through the water curtain, the paint mist is “scrubbed” from the air and carried to a sump basin usually located below the paint spray booth. In this area, the paint particles are separated from the water so that the water may be recycled and the paint particles disposed of.
The term “paint” as used herein is intended to encompass a mixture of resin, pigment, and a suitable liquid vehicle that is reasonably fluid and provides a thin and adherent coating when applied to a substrate. As such, the term “paint” is intended to encompass paints, lacquers, varnishes, base coats, clear coats, primers and the like.
Paint is a tacky material and it tends to coagulate and adhere to the spray booth surfaces, particularly in the sump and drain areas, and must constantly be removed from the sump to prevent clogging of the sump drain and recirculating system. In order assist in the removal of the oversprayed paint from the air and to provide efficient operation of paint spray booths, detackifying agents are commonly employed in the water used in such systems, and are typically incorporated into the water wash recirculated in the paint spray system. Detackifying the paint eliminates or minimizes the adhesive properties, or tackiness, of the paint, thereby preventing the oversprayed paint from adhering to the walls of the spray booth.
One of the difficulties with recovering paint overspray in a water wash spray booth as described above is the limited amount of paint which can be incorporated into the water. As such, detackifying agents should have a high load capacity, such that the water wash recirculated through the spray booth can detackify, coagulate and flocculate a high volume of oversprayed paint before exhaustion.
Moreover, in recent years, the need to reduce solvent emission has resulted in the reduction of solvent-based or solventborne paints, and an increase in the use of water-based or waterborne paints. The organic content in solvent-based paints, however, requires the use of different detackifying processes in paint spray booths.
For example, U.S. Pat. No. 5,259,976 discloses the use of cationic polymers such as acrylamide polymers for detackifying paint and improving paint spray booth efficiency, and using sodium aluminate to adjust the pH of the system. U.S. Pat. No. 5,019,138 discloses the use of an organic solvent, i.e., N-methyl pyrrolidone, to scrub the paint overspray from the surrounding air. However, the use of high quantities of organic solvent needed for this process is expensive and a potential health and environmental hazard. In addition, such detackifying agents are not effective for detackifying both water-based and solvent-based paints.
U.S. Pat. No. 5,223,141 discloses a method for removing and recovering solvent-based paint overspray through contact with an agitated dispersion of an organic solvent in water, and then allowing the dispersion to phase separate, for separation of the organic phase from the aqueous phase. Such dispersion, however, is often difficult to separate for removal of the paint from the water.
U.S. Pat. No. 4,888,386 discloses a composition for use in detackifying both waterborne and solvent enamels, which includes a melamine-formaldehyde polymer, a polyvinyl alcohol and a styrene acrylate copolymer. Such materials, however, are not readily biodegradable, and therefore pose environmental concerns for disposal.
Accordingly, a need exists for a composition which is useful for detackifying both water-based and solvent-based paints, which is capable of effectively decreasing emulsion formation in solvent-based paint denaturant systems, and which is biodegradable.